What Is The Greenhouse Effect?

The Greenhouse Effect is the atmosphere’s ability to trap heat from the sun, which causes the Earth’s climate to be warmer and more stable than it otherwise would be.

Understanding The Atmosphere

Our atmosphere acts like glass on a greenhouse, allowing light and heat to penetrate and warm the Earth while slowing the radiation of heat back out into space.

This effect is essential for life on Earth as we know it, and it all depends on a fragile layer of gas. The atmosphere’s heat trapping capacity is significant given how small the atmosphere is relative to the Earth. If you imagine the Earth is the size of an orange, a piece of paper wrapped around the orange would represent the relative thickness of the Earth’s atmosphere.

How the Atmosphere Traps Heat

The Sun radiates heat and light in enormous amounts. This energy is comprised largely of short wavelength radiation which is able to pass through the gases in our atmosphere to reach the earth. When the sun’s energy reaches the Earth it bounces back out toward space as long wavelength, low energy radiation.

Our atmosphere traps some of the energy, like the glass of a greenhouse. As a result, not all of the long wavelength radiation is able to radiate freely back out into space. The gases absorb the long wavelength radiation, thus keeping the sun’s energy inside our atmosphere, which warms the Earth.

As we add more greenhouse gases to the atmosphere, it is as if we are adding extra panes of glass to a greenhouse, thus increasing the atmosphere’s ability to trap and hold heat.

Importance of the Greenhouse Effect

Mars and Venus are the two planets closest to Earth in the solar system. The differences in the atmospheres of Venus, Earth, and Mars illustrate the importance of the greenhouse effect:

  • Mars has a thin atmosphere due to its a weak gravitational pull. The greenhouse effect on Mars is thus very weak, and the surface temperature is, on average, about -50 degrees Fahrenheit.
  • Venus’ has a very thick atmosphere that is made up mostly of carbon dioxide. As a result, the surface temperature is higher than the melting point of lead!
  • Earth’s atmosphere is thinner than Venus’and thicker than Mars’ and is made up almost entirely of nitrogen and oxygen. Clearly a different atmosphere would mean a very different circumstance on the surface of the Earth.

Global Warming Theory

Svante Arrhenius proposed the theory in the 1890s while working as a chemist in Sweden. He posited that different gasses might retain heat in the Earth’s atmosphere, and thus cause global warming.

Arrhenius undertook painstaking calculations of the energy entering Earth’s atmosphere and estimated how seemingly small changes in its composition might change the balance of incoming energy with what radiates back out into space. His general theory appears correct, though it was ignored for many decades.

Modern scientists have taken careful measurements of greenhouse gas concentrations in the Earth’s atmosphere as well. Not only are the concentrations increasing, but the rate of increase is accelerating. Looking at the long history of our planet Earth, scientists have come to understand that the balance of greenhouse gases in our atmosphere has in the past correlated very closely with warming and cooling periods.

Earth has had periods of rapid change when carbon dioxide levels have risen. In these periods ocean currents, air currents and weather patterns have changed very rapidly all over the Earth. In past eons when carbon dioxide levels in the atmosphere have decreased, the Earth has entered ice ages.

Scientists are deeply concerned that we may be nearing a tipping point where such dramatic changes of climate and weather will occur again.


Author: Brown, Nathan. A Cooler Climate, 2008.

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